1. Field of the Invention
The present invention relates to an organic light emitting display panel, and more particularly, to an active matrix organic light emitting display panel having a structure capable of minimizing a resistance of a power line.
2. Discussion of the Related Art
Cathode ray tube (CRT) has drawbacks due to its heavy weight and large volume. Thus, many efforts have been made to research and develop various flat display devices, such as liquid crystal display (LCD) devices, field emission display (FED) devices, plasma display panel (PDP) devices, and organic light emitting display devices, which is also often referred to as organic electro luminescent display devices, as a substitute for CRT devices.
An organic light emitting display device is a self-luminescent type display. In general, the organic light emitting display device emits light by injecting electrons from a cathode and holes from an anode into an emission layer, combining the electrons with the holes, generating an exciton, and transitioning the exciton from an excited state to a ground state. Accordingly, the organic ELD does not require an additional light source and has a light weight, thin profile, and compact size. Further, the organic ELD can operate using a low DC voltage, thereby having low power consumption and fast response time.
FIG. 1 is a schematic diagram illustrating an active matrix organic light emitting display panel according to the related art. In FIG. 1, an active matrix organic light emitting display panel includes gate lines GL1 . . . GLm and data lines DL1 . . . DLn arranged on a substrate 10 and intersecting each other, and pixel elements PEs arranged at intersecting portions between the gate lines GL1 . . . GLm and the data lines DL1 . . . DLn. A power line 15 for applying a pixel power from a power supply unit 13 is connected to each pixel element PE.
In particular, the pixel power is applied through a pad (not shown) formed on the panel to the power line 15. When a gate signal of a gate line GL is enabled, a corresponding pixel element PE is driven to generate light corresponding to the strength of a pixel signal of a data line DL. A gate driver 12 is connected to the gate lines GL1 . . . GLm to sequentially drive the gate lines GL1 . . . GLm, and a data driver 14 is connected to the data lines DL1 . . . DLn to supply pixel signals through the data lines DL1 . . . DLn to the pixel elements PEs.
FIG. 2 is a circuit diagram illustrating a pixel element of the active matrix organic light emitting display panel shown in FIG. 1. As shown in FIG. 2, the pixel element PE includes an organic light emitting diode OLED or an electro luminescent cell connected to a ground source GND, and an organic light emitting diode (OLED) driving circuit 16 connected between the organic light emitting diode OLED and the corresponding data line DL.
The OLED driving circuit 16 includes a second PMOS thin film transistor (TFT) T2 connected between the organic light emitting diode OLED and a power line VDD to function as a driving element for the organic light emitting diode OLED, a first PMOS TFT T1 connected between the corresponding data line DL and a gate electrode of the second PMOS TFT T2 to function as a switching element for the organic light emitting diode OLED, and a capacitor Cst connected between the power line VDD and a drain electrode of the first PMOS TFT T1.
Thus, when a scan signal, e.g., a LOW signal, from the gate driver 12 (shown in FIG. 1) is inputted to the corresponding gate line GL, the first PMOS TFT T1 is turned on. When the first PMOS TFT T1 is turned on, a video signal of a predetermined strength that is inputted from the corresponding data line DL in synchronization with the scan signal flows through the first PMOS TFT T1 and is then charged in the capacitor Cst. That is, the capacitor Cst is charged with the video signal supplied from the corresponding data line DL, while the LOW signal is inputted to the gate line GL. Further, the capacitor Cst holds the video signal for one frame period. Accordingly, the capacitor Cst supplies the video signal to the organic light emitting diode OLED during one frame period.
However, a voltage drop across the power line VDD must be small in order to uniformly maintain an image quality of the active-matrix organic light emitting display panel. Yet, due to the structure of the active-matrix organic light emitting display panel according to the related art, there is a limit in how much the width or thickness of the power line could be increased for keeping the voltage drop across the power line small. Accordingly, a large voltage drop across the power line cannot be avoided, thereby causing a large difference between voltages applied to pixels connected respectively to the first and last stages of the power line. Thus, an image quality of the organic light emitting display according to the related art is not uniformly maintained.
FIG. 3 is a schematic plan view illustrating a power line of an active matrix organic light emitting display panel according to the related art. In FIG. 3, a lower substrate 10 and an upper substrate (not shown) are attached together and encapsulated so as to prevent moisture and oxygen from infiltrating into the organic light emitting display panel. In particular, the lower substrate 10 and the upper substrate (not shown) are attached together by a sealant coated on a seal pattern portion 16 at an edge portion of the lower substrate 10. For example, the sealant is material having a property of being hardened by UV light.
A region of the panel includes a display region 12 corresponding to a center portion of the lower substrate 10, and a non-display region 14 between the display region 12 and the seal pattern portion 16. In particular, an image is displayed by pixels (not shown) arranged in the display region 12 in a matrix pattern.
In addition, a power supply unit (not shown) supplies a pixel voltage through a pad 18 to a power line 17, and the power line 17 sends the pixel voltage to the pixels arranged in the display region 12. The power line 17 includes a routing line 13 connected directly to the pad 18 and formed in the non-display region 14, and pixel lines 15 connected to the routing line 13 to apply a pixel voltage to the pixels in the display region 12.
For example, the routing line 13 receives the pixel voltage from the pad 18 and applies the received pixel voltage through the pixel lines 15 to the pixels. Thus, the width or thickness of the routing line 13 of the power line 17 may be increased to reduce the voltage drop across the power line 17 in order to uniformly maintain an image quality of the active-matrix organic light emitting display panel.
However, since the routing line is formed in the non-display region, and the non-display region of the panel is kept small to maximize the display region, the structure of the active-matrix organic light emitting display panel according to the related art cannot sufficiently increase the width or thickness of the power line. Thus, the organic light emitting display according to the related art has a large voltage drop across the power line and is unable to uniformly maintain the image quality.